The British captain of a cruise ship that failed to rescue three stricken Panamanian fishermen adrift in the Pacific Ocean is said to be devastated by accusations he ignored calls for their rescue.

Princess Cruises, the operator of the Star Princess, blamed a “breakdown in communications” for the tragedy, saying passenger reports that they had seen a boat in distress never made it to the captain or the officer on duty.

But a passenger who helped alert the ship’s crew to the fishing boat has rejected the explanation as “not credible”.

Two of the three men on the drifting boat later died of dehydration, one within hours of the Star Princess passengers attempting to raise the alarm after spotting the lost boat.

The story of Adrian Vasquez, the 18-year-old hotel worker who survived for 28 days adrift in the Pacific, was a global news story after his rescue near the Galapagos islands. But the Guardian revealed earlier this week that the fishing boat, the Fifty Cents, had been spotted on 10 March by three birdwatchers on the Star Princess, but the liner failed to stop. Later the same night, Oropeces Betancourt, 24, died of dehydration. The youngest fisherman, Fernando Osorio, 16, died on 15 March, suffering from dehydration, sunburn and heatstroke.

The cruise line, which is owned by Carnival – the same corporation behind the operators of the Costa Concordia which capsized this year – said investigations were still trying to establish the exact circumstances of the incident.

“Princess Cruises deeply regrets that two Panamanian men perished at sea after their boat became disabled in early March,” a statement said. “The preliminary results of our investigation have shown that there appeared to be a breakdown in communications in relaying the passenger’s concern.

“Neither Captain Edward Perrin nor the officer on the watch were notified. Understandably Captain Perrin is devastated that he is being accused of knowingly turning his back on people in distress. Had the captain received this information he would have had the oportunity to respond.”

It continued: “We all understand that it is our responsibility and also the law of the sea to provide assistance to any vessel in distress, and it is not an uncommon occurrence for our ships to be involved in a rescue at sea.

In fact, we have done so more than 30 times in the last 10 years. We deeply regret this incident and are continuing our investigation to fully understand the circumstances.”

But one of the birdwatching passengers who saw the boat said Carnival’s explanation didn’t “stack up”. Jim Dowdall, 54, an environmental consultant from Dublin, said: “How does a junior officer phone the bridge and come to look two times and there’s no communications? Whoever the officer on the bridge was should have taken action himself or alerted the captain.” Judy Meredith, 65, from Bend, Oregon, said she contacted a crew member, who told her he was relaying her concerns to the bridge. She said it was “horrific news” when she found out the full details of the tragedy unfolding on the small boat, and discovered that two young men had died in such desperate circumstances, and “both could have lived, had the cruise ship responded to our urgent request”.

Don Winner, a Panama-based, English-language blogger, later tracked down Vasquez, who confirmed that he and his friends had seen the cruise ship and had signalled frantically. He also confirmed that a picture taken by the cruise passengers was of his boat.

Jeff Gilligan, 61, from Portland, Oregon, who was travelling with Meredith, said a member of the crew had looked through their binoculars at the boat. “He said he could see what we were describing. We suggested that the people from the bridge came down and looked. He said they had binoculars … We were convinced the bridge knew what was happening and thought maybe it took a while to turn around. But after a while we realised it wasn’t turning. But we told ourselves that this cruise ship would have radioed coastguards.”

Dowdall, 54, said that the crew member he spoke to had a naval uniform “with stripes on his shoulder” and said he was at the Future Cruise Sales desk. “He came out a second time and looked through our scopes again, as if he’d been told to double check. He was on a mobile or walkietalkie, in communication while we were looking. All the time the boat was getting further and further away.”

He said while it was too late for the two Panamanian men, “I would just hope they would respond by putting some formal protocol in place so that it never happens again — training right from the most junior crew member to the captain”.

“We did have optics, we had the telescopes, We demonstrated the boat was there, not just something we imagined.”

On returning home and learning of the Panamanian men’s fate, Meredith was told by a Princess Cruises customer services representative that the ship’s log recorded that the Star Princess had “made contact” with the fishing boat and they were “waving to thank them”.

While Princess have yet to respond to questions on this issue, Jeff Gilligan said he had been called by a representative who said they had mistakenly confused the dates, an explanation he said was “plausible”.

But, he said, from their conversation “they want to suggest we didn’t communicate it. We did communicate it, very clearly. That’s the whole problem, that they didn’t take people seriously.”